1. Field of the Invention
This invention relates to the preparation of polyisocyanurate polymers such as polymer foams, and is more particularly concerned with use of a class of catalysts which promote the trimerization of polyisocyanates to polyisocyanurate polymers.
2. Description of the Prior Art
Polyisocyanurate polymers such as rigid polyisocyanurate foams are known in the art. The prior art discloses methods for preparing such polymers by reacting an organic polyisocyanate with a polyol utilizing a polyisocyanurate group formation catalyst. Foams are prepared by effecting such reaction in the presence of a blowing agent. In the optimum situation the isocyanurate catalyst utilized promotes formation of both isocyanurate linkages and urethane linkages to produce urethane-modified polyisocyanurate polymers. See, for example, U.S. Pat. Nos. 3,516,950, 3,580,868; 3,620,986; 3,625,872; 3,635,848; 3,725,319; and 3,745,133.
In particular, the use of quaternary ammonium compounds such as quaternary ammonium hydroxides, alkoxides, and aryl oxides such as phenoxides are disclosed as useful catalysts in reactions involving organic isocyanates, such as in the formation of polyisocyanurates, polyurethanes and polyurethane-polyisocyanurate resins. Representative art includes, for example, German Offen. 2,527,241; U.S. Pat. Nos. 2,779,689; 2,981,700; 3,726,816; 3,010,963; 3,108,975; 3,954,684; 3,892,687; 3,928,256; 3,933,699; and 3,980,594 and U.S. Published Patent Applications Ser. Nos. B497,194 and B490,946.
It has been found here, however, that the use of the above quaternary compounds, particularly in preparing urethane-modified polyisocyanurate polymers have a number of drawbacks. The hydroxides and alkoxides particularly in many instances promote too rapid a reaction, leading to problems of control in preparing the polymers. In other instances, catalysts of this type are not sufficiently heat stable and/or, are relatively incompatible in the polymer-forming systems used. Again, catalysts of this type in some instances are difficult to prepare and their use then becomes somewhat uneconomical. Lastly, many prior art catalysts of this type do not produce the desired high concentration of isocyanurate linkages in the polymer unless relatively large amounts of catalysts are used, and in many cases even use of such high amounts of catalyst does not achieve the desired aim of a polymer containing substantial numbers of isocyanurate linkages.
We have now discovered that these and other drawbacks of prior art catalysts have been overcome by resort to the particular class of polyisocyanurate catalysts defined here.